Surface flaw detection apparatus and method which energize the surface of a test piece with energy of one mode and detect energy of an orthogonal mode which results from perturbation of the incident current in the presence of a surface flaw are well known as disclosed in an article by R. J. Hruby and L. Feinstein, "A Novel Nondestructive, Noncontacting Method of Measuring the Depth of Thin Slits and Cracks in Metals", Rev. Sci. Insts., Vol. 41, No. 5, pp 679-683 (May 1970), and in U.S. Pat. No. 3,532,973, issued Oct. 6, 1970, entitled, "Microwave Flaw Detector", by L. Feinstein and R. J. Hruby. With such prior art arrangements surface illumination of the test piece with microwave energy is provided by a transmitting/receiving horn. Orthogonal mode signals produced as a result of the transmitted signal are received by the horn and provide an indication of surface flaws. The horn, however, is capable of illuminating only a small surface area, on the order of 2 cm in diameter, and extensive mechanical scanning of the horn relative to the total surface area of interest is required. With the present invention, using parallel strip transmission lines, an extended linear area may be covered, thereby greatly reducing the scanning necessary for inspection of the total surface area of interest.